Modern electronic circuits sometimes require that a high-voltage-related signal (even as high as 500 V) be converted to a signal that is low voltage compatible with normal digital circuits (typically operating between 0 and 5 V). Such is the case, for example, with low-side or high-side power MOS transistor drivers which supply digital diagnostic signals (e.g. relative to short-circuiting, correct open/close operation of the power MOS transistor, etc.) which may selectively assume two different high-voltage-related levels (e.g. 500 and 495 V), and the level of which must therefore be shifted and related to ground for the signals to be processed by normal digital circuits, e.g. microprocessor systems.
In some cases, the need arises for a shift circuit including active, low breakdown voltage components, as, for example, when the fabrication technology available does not permit the use or formation of PNP bipolar or P-channel MOS transistors capable of withstanding the high input voltage.